Neanderthals and Denisovans, two archaic hominid species, have been shown by genetic tests to have interbred with human migrants in Europe and Asia. (Source: Corbis)

Researchers speculate that such sexual attractions between the species were rare, but that the children were much more genetically fit, so came to dominate the population. (Source: Google Images)

The highest rates of Denisovan DNA occurrence were found in the DNA of natives of Papua New Guinea. (Source: Flickr)

The immune proteins our hominid relatives gave to us during interbreeding made us hardier and more resist to potentially deadly infections. (Source: Paul de Bakker)

Turns out Europeans and Asians may be the least "genetically pure" homo-sapiens

It turns
out that European DNA, like that of Asians and Africans, has traces ofarchaic hominidsmixed in with the familiarHomo sapien-specific
stretches.

Thesequencing of the Neanderthal genomehas led to some incredible discoveries -- among them, that humans
were having sex with Neanderthals. A pair of new studies has shown thatNeanderthal
genes aren't evenly distributed throughout the entire human population --
rather some populations have more or less of them.

A new study, whose senior author is Peter
Parham, a professor of cell biology, microbiology and immunology
at theStanford
University School of Medicine, examines how interbreeding with our
closely related hominids led to a superior human immune system.

Svante Pääbo, director of the Department of Genetics
at theMax Planck
Institute for Evolutionary Anthropologyand senior author onthe paper[abstract] detailing the original Neanderthal genome draft,
suggests that one of two possibilities occurred. Either migrants to Asian
and Europe broadly had sex with Neanderthals or just a few did, but whose
progeny survived in greater numbers, passing on the early hominids' genetic
material. Researchers believe the latter explanation is more likely the
case.

Humans are thought to have migrated from Africa around 67,500 years ago,
spreading to Asia and Europe. In these regions they encountered
Neanderthals and Denisovans -- another archaic hominid, who they at least
occasionally engaged in sexual intercourse with. Interbreeding is thought
to have occurred starting around 50,000 years ago.

Those hairy charmers passed something valuable along to the migrants --
improved immunity. Many of Eurasians' HLA genes -- fast evolving
human immune system components -- are thought to have been "borrowed"
from the Neanderthal and Denisovan genome.

It found that one Denisovan-derived gene -- HLA-A -- was 95 percent
likely to occur in residents of Papua New Guinea, 70 percent in residents of
China, 50 percent in Europe, and virtually non-present in Africa.

The genes are thought to have conferred improved survival rates on the
migrants, as they gained defenses against local diseases, which took their
archaic hominid co-inhabitants millennia to develop.

Africans, who never personally interbred with the Denisovans and
Neanderthals did receive a bit of these genes second hand, from migrants who
returned to the region around 10,000 years ago. And they are thought to
have an even stronger and more diverse immune system, as they bred withother species of archaic hominids, which were native
to Africa.

Previous studies have shown that non-Africans have around 4 percent
Neanderthal genes, while Melanesians -- natives of Indonesia and the
surrounding islands -- also have 4 to 6 percent of their genes derived from
the Denisovans.

The study on the project ispublished[abstract] in the prestigious peer-reviewed journalScience.

The new work could offer some additional explanation of why Native
Americans may have been so susceptible to diseases brought to the New
World by Europeans and Africans. Native Americans may have missed much of
the interbreeding opportunities. Thus while they may be the most
"pure" examples ofHomo sapiens DNA,
that may have proved fatal to many of them.

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